He was awarded his pilot wings at Webb Air Force Base, Texas, in September 1952, continuing through December 1952 in All-Weather Interceptor School and Gunnery School. From February 1953 to August 1955 during the Korean War, Day served two tours as a fighter-bomber pilot, flying the Republic F-84 Thunderjet in the 559th Strategic Fighter Squadron. Promoted to captain, he decided to make the Air Force a career and was augmented into the Regular Air Force. He was assigned to the 55th Fighter Bomber Squadron. He then trained to fly the F-100 Super Sabre in 1957 while stationed at Royal Air Force Wethersfield in the United Kingdom through June 1959. During this time he was forced to bail out when his jet fighter caught fire. His parachute canopy failed to blossom, making him the first person to live through such an event. According to Day, a pine tree cushioned his fall. Day was assistant professor of aerospace science at the Air Force ROTC detachment at Saint Louis University in St. Louis, Missouri, from June 1959 to August 1963. Anticipating retirement in 1968 and now a major, Day volunteered for a tour in South Vietnam and was assigned to the 31st Tactical Fighter Wing at Tuy Hoa Air Base in April 1967. At that time, he had more than 5,000 flying hours, with 4,500 of them in fighters. On 25 June 1967, with extensive previous service flying two tours in F-100s, Major Day was made the first commander of Detachment 1, 416th Tactical Fighter Squadron, 37th Tactical Fighter Wing based at Phu Cat Air Base. Under the project name Commando Sabre, twin-seat USAF F-100Fs were evaluated as a Fast Forward Air Controller (Fast FAC) aircraft in high threat areas, given that F-4 Phantom II aircraft were in high demand for strike and Combat Air Patrol (CAP) roles. Using the call sign Misty, the name of Day's favorite song, his detachment of four two-seat F-100Fs and 16 pilots became pioneer "Fast FACs" over Laos and North Vietnam. All Misty FAC crews were volunteers with at least 100 combat missions in Vietnam and 1,000 minimum flight hours. Tours in Commando Sabre were temporary and normally limited to four months or about 60 missions. Prisoner of war On 26 August 1967, Major Day was flying F-100F-15-NA, AF Serial No. 56-3954, call sign Misty 01, on his 26th Fast FAC sortie, directing a flight of F-105